1. Field of the Invention
The present invention relates generally to hard copy apparatus, more particularly to print media sensing and, more specifically, to a transmissive optical sensing method and apparatus for print media sheet recognition.
2. Description of the Related Art
In designing paper path for hard copy apparatus, a designer must address the problem of print media (hereinafter referred to generically as xe2x80x9cpaper,xe2x80x9d regardless of form, e.g., plain paper, special media, envelopes, and the like as would be common to the state of the art) recognition and positioning, multiple sheet picks, and transport to and through the printing zone. It is rare that multiple sheet picks present perfectly registered sheets of paper where a printing errorxe2x80x94generally print registration on the pagexe2x80x94will not occur. Therefore, when multiple sheets are overlapped, state of the art paper length sensing devices generally indicate a single sheet that is longer than the actual media in the input supply because the commonly used optical detectors or opto-mechanical interrupters inherently do not have the capability to sense the presence of two overlapped sheets of paper since the overlapped region between the two sheets generates the same signal as a single sheet. Exemplary optical media sensing methods and apparatus are shown in U.S. Pat. No. 5,135,321 (Olsen et al.), U.S. Pat. No. 5,466,079 (Quintana) and its divisional, U.S. Pat. No. 5,564,848 (each assigned to the common assignee herein and incorporated by reference in their entireties).
Multiple sheet picks effect a throughput loss as any print is likely to be mis-registered, requiring a reprinting.
There is a need for a method and apparatus which has the capability to view overlapped print media as being different than a single sheet. Moreover, such an apparatus is useful in the detection of top-of-form and bottom-of-form in the feeding and transport of multi-page printed form sheets are being fed and small overlaps are intentional. Furthermore, such an apparatus is useful in detecting the gap length between tail-gating sheets of paper.
In a basic aspect, the present invention provides a print media sensor device, including: mounted for bracketing a print media transport path, at least one emitter for directing a light beam across the transport path, the light beam having predetermined intensity and wavelength for penetrating print media, and aligned with the emitter, receptor mechanisms for receiving the light beam, wherein the receptor mechanisms provides a first output signal indicative of no paper breaking the beam, a second output signal indicative of a single sheet of print media interrupting the beam, and at least one other signal level indicative of multiple sheets of print media interrupting the beam.
Another basic aspect of the invention is a method of detecting print media in a print media path, including the steps of: positioning a transmissive light sensor along the print media path; calibrating the sensor for providing a first signal indicative of no print media within the field-of-view of the sensor, a second signal indicative of one sheet of print media being within the field-of-view of the sensor, and at least a third signal indicative of multiple sheets of print media being with the field-of-view of the sensor, wherein a change from the first signal is also indicative of a leading edge position of the print media in the print media path and a change from the second signal to the first sign is indicative of a trailing edge position of the print media in the print media path.
Another basic aspect of the present invention is a hard copy apparatus having a predefined paper path including a region upstream of a printing zone of the apparatus, associated with the printing zone, mechanisms for printing on paper, mechanisms for transporting paper from an upstream side of printing zone to an input of the printing zone, and paper position detector and indicator mechanisms, the mechanisms including: aligned with respect to associated with the predefined paper path region, a sensor having at least one light transmitter and at least one light receptor respectively positioned bracketing a predetermined position of the region, wherein the receptor provides signals indicative of conditions within the paper path including a first signal indicative of no print media within the field-of-view of the sensor, a second signal indicative of one sheet of print media being within the field-of-view of the sensor, and at least a third signal indicative of multiple sheets of print media being with the field-of-view of the sensor, and wherein a change from the first signal is also indicative of a leading edge position of the print media in the print media path in the field-of-view and a change from the second signal to the first signal is indicative of a trailing edge position of the print media in the print media path within the field-of-view.
Some of the advantages of the present invention are:
it provides an substantially immediate detection of a multiple print media sheet pick;
it provides leading edge and trailing edge detection;
it provides a means for top-of-form and bottom-of-form detection;
it provides improvement in media edge detection for full-bleed printing; and
it provides for improvements to hard copy apparatus throughput.
The foregoing summary and list of advantages is not intended by the inventor to be an inclusive list of all the aspects, objects, advantages and features of the present invention nor should any limitation on the scope of the invention be implied therefrom. This Summary is provided in accordance with the mandate of 37 C.F.R. 1.73 and M.P.E.P. 608.01(d) merely to apprize the public, and more especially those interested in the particular art to which the invention relates, of the nature of the invention in order to be of assistance in aiding ready understanding of the patent in future searches. Other objects, features and advantages of the present invention will become apparent upon consideration of the following explanation and the accompanying drawings, in which like reference